Method and apparatus for sound reproduction



July 7, 1931 0. SANDVIK METHOD AND APPARATUS FOR SOUND REPRODUCTION Filed March 21, 1930 uu' in gwvwnlioz f 0H0, Sandvik.

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SATES PATENT F F lCE OTTO SANDVIK, OF ROCHESTER, NEH? YORK, ASSIGNOR TO'EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEV YORK METHOD AND APPARATUS FOR SOUND REPRODUCTION Application filed March 21, 1930. Serial No. 437,859.

This invention relates to the method of and apparatus for recording sound on photographic sound records and the reproduction of sound therefrom.

In apparatus for photographically recording and reproducing sound it is essential, especially in the case of portable devices, to reduce the equipment contained-therein to the lowest possible amount. It has, however,

been customary in the past to provide such apparatus with a lamp or other suitable source of radiations, and in addition to provide one or more electron discharge devices to amplify the electric current utilized in recording and reproducing. In accordance with one feature o f the present invention it is proposed to utilize the cathode or heater element of one of the electron discharge de vices of such apparatus as a source of radiations whereby the need of a separate lamp or other source is obviated. This results in the combined advantage of reducing the size of the equipment and the power consumption for it not only eliminates a lamp or other radiant source but in addition eliminates the battery or other source of current necessary to operate it. A further feature of the invention relates to the arrangement of the anode and control electrode with respect anode or control electrode thereby preventing any shadow of these elements in the radiations transmitted by the cathode.

For a clearer understanding of the'invention reference is made to the drawings in which Fig. 1 is a diagrammatic showing of one arrangement according to the present invention for photographically recording sound while Fig. 2 is a diagrammatic showing of a photographic reproducing system including the present invention; Figs. 3, 3A, 4, 4A and 5 represent different forms of an electron discharge device in which the cathode or its heater element is arranged to serve as a source of radiations of suificient intensity to photographically record sound, and Fig. 5A is an end view of the electrodes of the device shown in Fig. 5.

In the photographic recording and reto the cathode or its heater such that the cathode or its heater is not obscured by the.

production or" sound, an intense source of light or other radiations must be provided ilraddition to some form of electron discharge amplifier utilized to amplify the weak sound-modulated current encountered in such systems. As shown in the systems of Figs, 1 and 2 it is proposed to utilize the cathode or its heater element of the electron discharge devices 6 and Tas a source of radiations. In the sound recording system of Fig. 1 the cathode 8 serves as a source of radiations which is imaged on theslit 9 of the support 10 by means of a condenser lens 11. As is well-known, the recording element 12 variably closes the slit 9 in accordance .with the sound-modulated radiations .which are imaged on the film l l by the objective lens 13. In such a system there is also provided a microphone 15 which is coupled ,to the input of the electron. discharge amplifier device 6, theoutput circuit of which includes the primary winding of a transformer. 6 having itssecondary winding connected inseries with the movable portion of the recording element 12. From the foregoing it will be understood how the .electron discharge device 6 functions not only as an amplifier but as a source of radiations .in a photographic sound recording'device.

Similarly in the photographic sound reproducing system showninFig. 2 the cathode or its 'heat erelement 17 of the electron discharge device 7 in the amplifier alsoserves as asourceof light or other radiations. As is well-known, the usual reproducing system in addition to asource of radiations, is provided with a condenser lens 18 which forms animage' of the light source on the slit 20 in the support :21 over which the film 22 passes. 'The sound images on the sound trackof the record 22 vary the intensity of radiations from the source which fall on the photoelectric cell 23 or. other radiation sensitiveeelement to develop very feeble electric currents varying in accordance with the in cident radiations. Since thesephotoelectric currents are very wealnthey must be amplified by at least one electrondischarge device 7 whiclixhas its :input circuit coupledIto-the photoelectric ,cell 23 and its output circuit Y coupled by a transformer 24 to a loud speaker or other sound regenerating device 25.

IVhile the electron discharge device of the present invention is not limited to any particular arrangement, as represented in Fig. 3, it may include a flat anode 26 and a cathode 27 separated by a grid 28 which may have the form of a screen or a flat coil formed of finely spaced turns of wire wound on two spaced supports. The cathode, anode and grid have their vertical supports mounted in a glass press 29. These elements thus mounted are all enclosed in a highly evacuated, transparent envelope 30. In Fig. 3A there is represented a modified form of the discharge device shown in Fig. 3 wherein the cathode is shown as directly heated. In Fig. 3A the cathode 27 is arranged to be heated by the heater 47. It will be understood that the cathode 27 is open on the side most remote from the anode 26 and grid 28 so that radiations from the heater are not obscured by any of these elements of the device.

The electron discharge device of Fig. 4 differs from that shown in Fig. 1 in that the grid 28a surrounds the cathode 27a and the anode 26a in turn surrounds both of these elements. The anode 26a is shown with a window 31 and at this point the turns of wire in the grid 28a are spaced so that the radiations from the cathode 27a may pass unobscured through this window. In the modilied device of Fig. 4A the window 31 is omitted and the radiations through the upper end of the device are utilized. In still a difierent form of the invention, represented in Figs. 5 and 5A, the horizontal cathode 27b is surrounded by a cylindrical grid 28?) and a cylindrical anode 266 both having windows such as 34: and 31b in registry.

While only the form of the device shown in Figs. 3 and 3A is arranged with a directly heated cathode and an indirectly heated cathe ode, it will be understood that the other forms of the device shown in Figs. 4, 1A and 5 may similarly be provided with an indirectly heated cathode, and it will be further understood that where the term cathode is used in the following claims it is intended broadly to cover the directly heated cathode and the heater element of an indirectly heated cathode.

The foregoing disclosure is merely for purposes of explanation and the invention is not to be limited thereby except as particularly set forth in the following claims.

What I claim is:

1. The method of reproducing photographic sound records which comprises transmitting light radiations varying in accordance with sound images on said records, translating said varying radiations into correspondingly varying electrical current, thermionically amplifying said varying our- 55 rent, translating said amplified varying current into sound, and utilizing the heated portion of the source of electrons employed in thermionically amplifying said current as the source of said light radiations.

2. The method of recording sounds on a photographic strip which comprises translating said sounds into corresponding electrical current, thermionically amplifying said current, utilizing the heated portion of the source of electrons used in thermionically amplifying said current, as a source of light radiations, modulating said light radiations in accordance with said amplified current, and photographing said modulated light radiations on said photographic strip.

3. In combination with a photographic sound record device employing a source of light, an amplifier including an electron discharge device having an anode, a control electrode and a substantially incandescent cathode, said cathode serving as the light source for use in said photographic sound record device.

4. In combination with a photographic sound record device employing a source of light radiations, an amplifier including an electron discharge device having an anode, a control electrode, a cathode, and a substantially incandescent heater for said cathode,

said heater serving as said source of light radlations.

Signed at Rochester, New York this lath day of March, 1930. r

. OTTO SANDVIK. 

